Update link for GitHub issue

Author: timholy

blog/_posts/2016-03-27-arrays-iteration.md

@@ -419,7 +419,9 @@ with generic code. It is possible that this is the right
 strategy. Alternatively, one can attept to devise an array API that
 handles all of these types (and hopefully more).
 
-In GitHub issue [#????](???), I propose one possible API that may
-resolve these challenges. However, it's quite possible that it is too
-limited for many practical problems. I encourage readers to join the
-discussion to help try to craft a suitable resolution.
+In GitHub issue
+[#15648](https://github.com/JuliaLang/julia/issues/15648), I propose
+one possible API that may resolve these challenges. However, it's
+quite possible that it is too limited for many practical problems. I
+encourage readers to join the discussion to help try to craft a
+suitable resolution.